Heat resistance is one of the main criteria for evaluating the performance of Engineering Plastics. The indicators that indicate heat resistance include heat distortion temperature, glass transition temperature, UL temperature index long-term continuous use temperature, melting point, and the temperature at which mechanical properties are reduced by half. The following table lists the thermal deformation temperature and long-term continuous use temperature of various engineering plastics.
| Heat Resistance of Various Engineering Plastics | ||
| Name | Heat Distortion Temperature (1.82MPa),℃ | Long-Term Continuous Use Temperature, ℃ |
| Nylon 6 | 63 | 65～130 |
| Glass Fiber Reinforced Nylon 6 | 206 | 65～130 |
| Polybutylene Terephthalate (PBT) | 60 | 120～140 |
| Glass Fiber Reinforced PBT | 212 | 120～140 |
| POM | 122 | 85～105 |
| Polycarbonate | 135 | 100～130 |
| Modified Polyphenylene Ether (MPPO) | 110 | 90～140 |
| Poly Alum | 175 | 140～150 |
| Polyether Alum | 203 | 170～180 |
| Polyphenylene Sulfide | 260 | 180～220 |
| Polyarylate (U Polymer) | 174 | 150～160 |
| Polyamideimide | 274 | 230～250 |
| Polyimide | 357 | 260～316 |
| Liquid Crystal Polymer (Xydar) | 310 | 210～260 |
| Teflon | 55 | 240～260 |
The softening of polymer compounds is essentially an increase in the degree of freedom of segment movement. If the factor that hinders the rotational freedom between the main chain atoms is increased, the heat resistance of the polymer compound will be improved. The main ways to increase this energy barrier are:
(1) Increase the intermolecular force (subvalent force) and increase the number of intermolecular hydrogen bonds.
Due to the hydrogen bonding force, the cohesion of the molecule increases, the crystallinity increases, and the melting point increases accordingly. In addition, increasing the dipole moment of the molecule (asymmetric structure) and introducing strong polar groups can also increase the attraction between molecules and increase the melting point.
(2) Improve the rigidity of the chain segment and reduce the flexibility.
For example, Polytetrafluoroethylene (PTFE) replaces the hydrogen atoms of polyethylene with fluorine atoms. Since the carbon-fluorine bond energy is greater than the carbon-hydrogen bond energy, the steric hindrance increases, which completely shields and seals the carbon-carbon bond on the main chain, increasing the The rigidity of the chain segment is increased, so the melting point increases from 137 °C of polyethylene to 327 °C. In addition, the introduction of aromatic nucleus groups with small flexibility and large steric barriers into the main chain structure can also improve heat resistance. For example, the glass transition temperature of polycarbonate is 142°C, the glass transition temperature of polyphenol is 185°C, and the melting temperatures of polyphenylene ester and polyphenylene ether sulfone are both greater than 450°C without a glass transition temperature, because they are mainly There is no hydrocarbon segment on the chain, and the rigidity is large.
Thermal cracking of polymer compounds is essentially the breaking of molecular chains. Therefore, the size of the bonding energy between atoms or groups on the chain link has a great influence on its heat resistance, and the chain link with low cracking energy should be avoided as much as possible on the main chain structure. The main measures that can be taken are as follows:
(1) Introduce atoms or groups with high bond energy to improve the stability of the main chain;
(2) The structure of the conjugated double bond system is introduced to improve the stability of the main chain;
(3) The main chain connection is not composed of a row of carbon-carbon monovalent bonds, but composed of two parallel rows of carbon-carbon monovalent bonds, carbon-carbon double bonds or carbon-nitrogen double bonds. , forming a five- or six-membered cyclic molecular chain or a double-stranded hank type molecular chain, so that it is not easy to break under high temperature or radiation.
